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KINESIOL 2C03 Midterm: Midterm 2

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Audrey Hicks

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Effect of Velocity of SSC Potentiation  A high velocity compared to a low velocity generates more ECC force  Isolated CON force decreases  ECC has more to ‘give’  CON has more to ‘gain’  Velocity of ECC affects SSC potentiation even if CON velocity doesn’t change  As velocity increases, force decreases o Using the SSC increases overall CON after ECC  > Relative (%) potentiation at higher velocities  Explains why SSC is most important in running, jumping, throwing, kicking (fast movements)  At a given velocity, ECC contractions can be submaximal or maximal Examples of Effect of ECC Force  Max ECC followed by max CON is done on isokinetic dynamometers (lab 2)  Sub max ECC followed by max CON done in throwing and jumping  Sub max ECC followed by submax CON done in weight training (several reps) When is SSC Inappropriate?  When time is needed for ECC phase and can’t be spared (backstroke push off)  When a rule forbids its use  When overuse can lead to injury o High impact aerobic and high velocity plyometrics (step classes)  Can create too much SSC (jump from too high) o Inhibition and can’t absorb shock Effect of Training of SSC  Increased ECC force (strength o Increased muscle size o Increased neural activity  Increased storage of elastic energy o Connective tissue/tendon (stiffer) o Cytoskeleton (stiffer)  Increased reflex potentiation o Increased neural activation  Ex, gymnasts and volleyball players were not inhibited by jumping higher o Training improved “shock absorption” o Able to use SSC more efficiently SSC and Efficiency  Efficiency = energy out/energy in x 100  Expressed as %  Rate of using 02 (metabolic rate and mechanical power)  More energy efficient when using the SSC o Increased ECC force from stretched CBs  No ATP cost, decreased overall elastic energy o Storage and release of elastic energy  No ATP cost, decreased overall elastic energy o Prevention of ‘wasted’ CB action taking up the SEC  More efficient use of ATP  Running vs. walking o Running uses more energy than regular walking (efficient) o Running uses same energy despite speed and time o Race walkers use the most energy (inefficient) o Running uses the SSC with bouncing Force-Length Relation (FLR)  Variation in muscle force (tension) at different muscle lengths  See graph on page 90  Passive force increases with length  Active force increases to optimal length and then decreases  Passive force: resistance of relaxed muscle to stretch (no active CBs)  Active force: produced by active CBs during contraction  Total force: active + passive force  Optimal length: length at which greatest active force occurs  Resting length: length at which passive force begins to develop  Relationship between optimal length and resting length varies in different muscles o Gastroc: resting length occurs then optimal length o Sartorius: Resting length at same time as optimal length o Semitendinosus: Optimal length then resting length  Working range of Force Length Relation (lab 3) – limits depend on muscle  Extensibility limit (muscle rupture) (flexibility) Mechanism for Variation in Passive Force  Exponential increase in resistance of relaxed muscle to stretch  Force collected in connective tissue, tendons and cytoskeleton Mechanism for Variation in Active Force  Plateau due to bare zone with no CBs  At optimal length o Optimal overlap of actin and myosin o All CBs can bind to actin o Maximal possible force  Greater than optimal length o Incomplete overlap of actin and myosin o Not all CBs can bind to actin o Decreased force  Less than optimal length o Actin filaments overlap with each other o ‘Disruption’ of CB bind to actin o Decreased force o Z-disks compress myosin filament o “Resistance” to sarcomere shortening o Decreased force Inter-Species Differences  Myosin Filament length – little variation  Actin Filament length – significant variation o Humans have greatest length o Frogs have shortest length o See different species lengths in page 99 Strength Curves  % maximum strength depends on joint angle  Peak or summit (pg 102) depends on action and joint  Variation in strength through range of motion  Depends on: o Force-Length Relation  Different muscles operate on different parts on the FLR  Pg 104 o Muscle Moment Arm  Perpendicular distance between the line of pull of the muscle and the joint centre  Torque = F x ma (Nm)  Changes throughout ROM  Smaller MA needs more force  Effect on torque depends on differences in force Interaction of MA and Force Length Relation  May not always contribute equally  Depends on muscle  Depends on weight on MA to force length relation Why are MAs so small?  Think of like fulcrum – weight needs to be closer to axis of rotation  Force and MA have to be equal to hold a weight statically  Pg. 109 Cost of Small Moment Arms  Result in decreased torque (strength) and increased injury o Avulsion: tendon and muscle detach from bone o Due to large muscle force needed for ‘modest’ torque  If MA increases, and ROM decreases, speed of joint motion decreases*** Advantage of Small Moment Arms  For the same amount of muscle shortening, increased range of motion and speed  Ex, muscles A and B have same cross sectional area and fibre length o B has twice the moment arm and twice the torque o B has to shorten twice as much as A for a given change in joint angle o B has half the angle of motion Other Influences on the Shapes of Strength Curves  Training o Neural Adaptations: recruiting, firing, first 6 weeks o Muscle Adaptations  Fatigue o Effect is much greater as muscle shortening increases  Injury o Nervous system doesn’t activate in fear of further damage (partial as well)  Maximal voluntary contraction (MVC) around 120 degree joint angle o Differs between men and women o Men have stronger elbow flexors (bodybuilders as well)  When bent and at max contraction pull is not as efficient o Bulge of muscle causes less efficient sarcomere shortening Strength Curves and Strength Measurements  Isometric Strength Measurement  Greater error in measurement to peak (ISO)  Peak strength is measure at same joint angle usually on summit  May not always have peak/’flat’ section  May have the same range but shorter contraction o More error, big difference in strength  Range of Movement (ex, hamstrings increase in strength as angle increases)  Most strength at close to full extension for hamstrings  Force increases with concentric and decreases with isometric? Strength Curves and Training Equipment  Ideal weight is close to matching strength  Cable lateral raises matches strength curve better than lateral dumbbells  Variable resistance pulley increases force required  Full extension of an elbow curl has a shorter radius  Full contraction of an elbow curl has a bigger radius  Strongest at 120 degrees, not when short for elbow curl  An isokinetic device automatically matches resistance to strength curve Neural Control and Motor Units  Anterior spinal cord is motor, posterior is sensory  Cord is made up of gray matter  Spinal cord diameter = 15 mm  NMJ diameter = 7 um  Muscle fibre diameter = 100 um  Motor unit = motoneuron + innervated muscle fibres  Motoneuron = cell body (soma) + axon (15 um diameter) o Diameter decreases with increased branching o Axons include many branches, one per muscle fibre  Motoneuron or motor neuron  Increased complexity decreases muscle fibres/ MU (MU size)  # of MUs depends on complexity of movement and muscle size  # of MUs/muscle determined by both the size of the muscle and the size of the MUs  Fibres of different motor units intermingle with each other  Overlapping of MU territories prodce the ‘mosaic’ look of a muscle cross section  All fibres of a motor unit are the same fibre type Motor Neuron Territory  750 MUs = 1/750 (.13%) of total number  If total area = 1000m2, each MU would occupy 1.3 mm2  Studies actually show territory to be 5 mm diameter, so area for each MU is 20 mm2  So each motor unit occupies 2% of muscle area instead of predicted .13 o ~15 x greater Purpose of large MU territories and intermingling of fibres of different units?  MU force is distributed over a large area  smoother contraction  May help delay fatigue: inactive and active fibres, or different fibre types share metabolites and capillaries Motor Unit Types  Slow twitch (ST) = Slow Oxidative (SO) = Type 1  Fast twitch (FT) = Type II = 2 subtypes o Fast Oxidative Glycolytic (FOG) = IIA o Fast glycolytic (FG) = IIB (IIX in humans)  Depends on training
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